Glaucoma is a disease of the eye in which intraocular structures critical to vision is irreversibly damaged. These structures include portions of the retina and especially portions of the optic nerve. Glaucoma, a treatable condition, is cited as the second leading cause of blindness in the United States. Several million people are affected. There are two major types of glaucoma, open angle glaucoma, and closed angle glaucoma. Open angle glaucoma, the most common type of glaucoma, occurs when the normal appearing outflow pathways malfunction such that the eye does not adequately drain fluid which results in an intraocular elevation of pressure. Elevated intraocular pressure (IOP) in most open-angle glaucoma is due to an obstruction of aqueous outflow localized predominantly at the juxtacanalicular trabecular meshwork (TM) and the inner wall of Schlemm's canal (SC).
Treatments for elevated IOP due to outflow obstruction include topical and systemic medications, office-based laser procedures, and risk inherent invasive surgical procedures (trabeculectomy/tube shunt). Examples of laser procedures include argon laser trabeculoplasty (ALT) and selective laser trabeculoplasty (SLT). More recently less invasive surgical procedures have been introduced into the treatment paradigms, commonly termed minimally invasive glaucoma surgery (MIGS), or micro-invasive glaucoma surgical procedures. Current approaches of IOP reduction by MIGS include increasing trabecular outflow by bypassing the juxtacanalicular trabecular meshwork (TM) and inner wall of SC, increasing uveoscleral outflow via suprachoroidal pathways, reducing aqueous production from the ciliary body, or creating an external, subconjunctival/suprascleral drainage pathway.
The general concept of MIGS is typically to bypass outflow obstruction and enable resumption of flow via the eye's intrinsic outflow system which is often intact and functional beyond the region of outflow obstruction, rather than creating alternative pathways which may have significantly greater short and/or long term risks.
MIGS procedures often involve visualization and access to the intraocular outflow system. Due to the shape of the cornea and the location of intraocular structures related to MIGS procedures in the region where the iris appears to meet the peripheral cornea, total internal reflection occurs and can prevent a surgeon from viewing those outflow structures that reside beyond the “critical angle” of the optical pathway, which in the context of the anterior chamber surgical procedures disclosed herein, can also be referred to as the “critical angle” of the anterior chamber optical viewing pathway. According to some embodiments, the optical pathway as disclosed herein can refer to the viewing of the anterior chamber angle structures and not the optical pathway of the eye's visual system, e.g. near the center of the cornea to the macula. As such, devices to allow visualization of those outflow structures are often necessary for a surgeon to perform MIGS procedures. Goniolenses, both direct (allowing a straight optical pathway for viewing those structures) and indirect (using mirrors to view those structures) function by overcoming total internal reflection. However, intraoperative use of goniolenses can require significant dexterity and a steep learning curve, which may limit successful MIGS procedures to certain skilled surgeons in at least some instances.
In at least some of these surgical procedures, a surgical opening is created through the trabecular meshwork and the inner wall of Schlemm's canal to enable improved fluidic access into Schlemm's canal in order to reduce intra ocular pressure. Prior approaches to accurately target Schlemm's canal are often less than ideal. Thus, it would be beneficial to provide methods and apparatuses that provide improved consistency and accuracy in targeting Schlemm's canal and other structures of the eye. Also, work in relation to the present disclosure suggests that at least some of the prior approaches may result in openings into Schlemm's canal at less than ideal locations, for example at locations which are far away from collector channels. Alternative MIGS devices which bypass Schlemm's canal and drain aqueous fluid into the suprachoroidal space can also benefit from targeted location placement by improving visualization of adjacent ocular structures. Examples of such implant devices include the intracanalicular iStent®, and iStent inject and the suprachoroidal CyPass® microstent. Excimer laser trabeculostomy (ELT) which creates patent channel openings into Schlemm's canal can also benefit from improved targeting and visualization of structures in the eye.
Current methods and apparatus for viewing structures of the eye near the irido-corneal angle, such as the trabecular meshwork and scleral spur, can be less than ideal in at least some instances. For example, a goniolens can be somewhat more difficult to use than would be ideal, and it would be beneficial to provide improved methods an apparatus for viewing the structures of the eye near the irido-corneal angle during surgery in this region.
In light of the above, it would be helpful to have improved methods and apparatus for imaging the eye during surgical procedures, targeting outflow structures of the eye such as Schlemm's canal, and determining target locations for openings through the trabecular meshwork and into Schlemm's canal to improve flow.